ABSTRACT
Objective: To study the hypoglycemic effects of soybean isoflavones (SI) and soyasaponins (SS) in diabetes, and their inhibitory activities on alpha-glucosidase (EC 3.2.1.20) and alpha-amylase (EC 3.2.1.1). Methods: GK/Jcl type 2 diabetic rats were given diet containing 20 g/kg of soybean hypocotyl extracts (SHE) for 20 weeks, then the blood glucose and oral glucose tolerance test were observed. SI and SS were isolated by ODS column chromatography and high-performance liquid chromatography (HPLC) from SHE. The inhibitory activities of each component of SI and SS against alpha-glucosidase and alpha-amylase were tested by colorimetric method. Results: SHE decreased blood glucose significantly in type 2 diabetic rats and improved glucose tolerance in both normal and diabetic rats. In alpha-glucosidase inhibitory assay, Group B, Group E and DDMP (2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one) saponins showed potent inhibitory activities with IC50 values of 10-40 靘ol/L. Isoflavone aglycones also showed potent inhibitory activities against alpha-glucosidase with IC50 values of 20-150 mol/L, while isoflavone glycosides showed a little lower potencies. Inhibition of SI and SS on alpha-amylase was low, and their inhibitory activities were about 10%~20% at the concentration of 1g/L. Conclusion: SI and SS may decrease blood glucose and improve oral glucose tolerance in diabetic rats, probably via the inhibitory effects on alpha-glucosidase and alpha-amylase.